by Cameron Miller
Climate change predictions for Southern California indicate a trend toward hotter, drier conditions, which are linked to increased wildfire patterns. The people, homes, and properties most at risk from wildfires are those in wildland-urban interface (WUI) zones. These areas, which are defined by the close proximity of human communities to vegetated areas of federally owned land, are becoming more popular than ever for new construction of homes and businesses. As of 2010, there were 12.7 million more homes and 25 million more people in WUI, than there were in 1990, a trend which has only increased in the last decade. A 2018 study published in the Proceedings of the National Academy Sciences demonstrated that about one third of homes in the US are within WUI zones.
These patterns of development and human habitation amid shifting climate conditions, mean that arborists, forest managers, and other tree care professionals, need to plan for the future by planting trees which can adapt to changing conditions. Planting adaptable tree species today will prove highly valuable in our ability to mitigate the worst effects of fires, droughts, and floods, and will help to ensure a more secure future on the land for the coming generations of human and non-human inhabitants in Southern California. When considering the appropriate trees for these conditions, Canyon Live Oak, Quercus chrysolepis, is a good candidate, for many reasons.
There are twenty species of oaks native to California that take a variety of forms, and fill a variety of ecological niches. Conservationists, native plant enthusiasts, and homeowners in Southern California, heap praises on the charismatic and lightning-limbed Coast Live Oak, Quercus agrifolia. For its beauty, ecological and historical importance, the Coast Live Oak is worthy of this praise, though the narrow spotlight on these trees has come at the expense of other important native oaks. The Canyon Live Oak has a high number of desirable characteristics, and deserves further consideration as a preferred landscape tree, equal to the Coast Live Oak. Due to its prompt regeneration response after fire, wide geographic distribution, high wildlife value, and variability of acceptable growing conditions, the Canyon Live Oak is a tree that landscapers, arborists, and other tree care professionals in Southern California should consider planting, especially in WUI zones.
The Canyon Live Oak grows under more variable conditions than any other oak in California, with a range extending 1,300 miles, from the Umpqua River in Oregon, down into Baja, Chihuahua, and Sonora in Mexico. It is the most widely distributed oak species within the state of California, and spreads from the Klamath mountains in Northern California, through the Coastal Ranges, Sierra Nevadas, and the Transverse Ranges of Southern California. In addition to the wide geographic range, Q. chrysolepis can grow from steep canyons at elevations as high as 9,000 ft, and as low as 300 ft. In the northern parts of its range, it receives as much as 110 inches of rain annually, while in the desert mountains, it can survive with as little as 6 inches. It can also thrive in a wide variety of soil types, from shallow and poorly developed soils with little fertility in rocky canyons, to deep and well-developed fertile soils at lower elevations.
Depending on the conditions in which it is grown, it can assume a variety of forms—from a shrubby thicket in chaparral plant communities, to large multi-trunked specimens in oak woodlands, and open-grown specimens up to 100 feet tall in savannah-type settings. Canyon Live Oaks are highly drought resistant, and they are able to persist by making the adjustment to limit their growth during drought periods. All of this flexibility, from acceptable soil type, to elevation, to annual precipitation, and morphological form, all point to a high degree of adaptability encoded in Q. chysolepis genetics. As we face uncertain conditions associated with climate change and increasing incursion by humans into previously wild areas, this broad adaptability is a highly desirable trait, to maintain living trees in our landscapes, trees that can withstand adverse and erratic conditions.
The Canyon Live Oak is an extremely important wildlife tree, providing habitat for mammals such as deer, bobcats, mountain lions, black bears, and badgers; for birds, such as the California spotted owl, Nuttall’s woodpecker, Baltimore oriole, and black-headed grosbeak. Each of its many morphological forms gives cover for different species of animal, from the smaller shrub form which acts as a haven for small mammals, to nesting and perching spaces for birds on larger Q. chrysolepis specimens.
The leaves and young stems are a preferred browse for black-tailed deer, and the large acorns are among the most nutritious of native acorns, with high levels of fats, fiber, carbohydrates, and protein.
The distinctive acorn cap lends to its other popular name, “Goldcup Oak”.
One of the most common forms of Q. chrysolepis is the multi-stemmed trunk, which is often a result of sprouting in response to animal browsing or top-kill from wildfire. Canyon Live Oaks resprout from their root crown, often within mere weeks of burning. After the Stanislaus Complex fire in 1987, 100% of observed top-killed Q. chrysolepis resprouted, and after the Village Fire in Angeles National Forest in 1975, 90% of top-killed Canyon Live Oaks resprouted within the following 18 months.
This ability to remain alive and to resprout is significant as Southern California, and especially those in WUI, face increased fire threats. Though a handsome, multi-trunk landscape specimen of Q. chrysolepis may be top-killed during a fire event, regrowth will occur more quickly on an established Canyon Live Oak, than growth on a replacement tree, due to the former’s older, intact root system. There may be an aesthetic and emotional loss to a community associated with losing a familiar tree form, but to see it resprouting quickly may provide some comfort after a damaging fire. These sprouts can re-grow up to several feet within a year. Part of the Q. chrysolepis’s ability to resprout is due to its impressive root system.
The roots of Canyon Live Oaks are fast-growing and extensive, and have been measured at depths up to 24 feet. This rooting habit is also of great benefit to help prevent flood-related erosion on hillsides. Fire-damaged areas where heavy vegetation losses leave vulnerable bare soil behind, are especially susceptible to damage from flooding. Durable trees like the Canyon Live Oak can help to protect communities from further devastation from floods, as their living roots can continue to hold the soil and mitigate mudslides and erosion during heavy post-fire rain events.
There are many challenges ahead for residents of Southern California which are related to climate change, wildfires, and floods. Tree care professionals are on the front lines of response, through their management decisions and public recommendations. The Canyon Live Oak is a valuable tree that can help to keep living green cover on our landscapes, preserve vulnerable soil, and provide for wildlife, in a wide variety of possible scenarios. It is a rugged, mercurial survivor of a tree species, and one that deserves more space in our landscapes.
